Less than a week after concerns about earthquakes dominated public hearings on renewing Diablo Canyon nuclear power plant’s operating licenses, the county Board of Supervisors on Tuesday will consider asking federal regulators to delay the process until more high-tech seismic studies can be completed.
Plant owner Pacific Gas and Electric Co. has proposed doing three-dimensional mapping of the ocean floor off the nuclear power plant. Such mapping and other state-of-the-art analysis would tell geophysicists more about the earthquake potential of the area around Diablo Canyon.
Supervisors will vote whether to send a letter to the California Public Utilities Commission urging the agency to approve PG&E’s request to have its customers pay for the $16.73 million studies, which are expected to take three years to complete.
The board will also consider sending a letter to the Nuclear Regulatory Commission asking that Diablo Canyon’s license renewal be postponed until the seismic studies are complete. Failing that, the letter would ask that the agency not complete the renewal process until the earthquake mapping is complete and its findings are integrated into the final decision.
Supervisor Adam Hill, whose district includes the power plant, has already sent a letter of his own asking for the delay. If approved, Tuesday’s letter would carry the full weight of the board and would become the official position of the county.
Hill renewed his request for a delay at an NRC public hearing last Wednesday in San Luis Obispo. “I do so because I believe that would be the most logical and responsible route,” Hill said.
NRC officials say they plan to respond to requests for a delay by the end of the month. PG&E opposes any postponement.
In a letter to the NRC, the utility noted that the last time license renewal applications were delayed was following the Sept. 11, 2001, terrorist attacks. Those attacks prompted the agency to require significant security enhancements at all of the nation’s 104 nuclear reactors.
The danger of earthquakes has been a major public concern about Diablo Canyon ever since the Hosgri Fault was discovered offshore of the plant during its construction. Since then, a series of events has heightened those concerns.
In July 2007, an earthquake fault ruptured beneath the world’s largest nuclear power plant in northwest Japan. The plant was able to shut down as planned, but the temblor caused a fire, and a small amount of radioactive water leaked into the ocean, said Eliot Brenner, NRC director of public affairs, who recently toured the Japanese plant.
According to reports, that plant was designed to withstand a 6.5-magnitude quake, but the fault produced a 6.8-magnitude quake. By contrast, Diablo Canyon is designed to withstand a 7.5-magnitude quake.
Late in 2008, the Shoreline Fault was discovered near Diablo Canyon. Less than a mile offshore, it is a strike-slip fault, meaning the sides move horizontally, and its tsunami potential is considered low. It could generate a 6.5-magnitude quake.
The fault is estimated to be from nearly two miles to more than eight miles below Earth’s surface and from nine to more than 15 miles long and could intersect the Hosgri fault.
That fault is 68 miles long and about three miles offshore. Recent studies have indicated that it’s also a strike-slip fault, meaning it is less likely to cause a tsunami than other types.
At Wednesday’s hearings, the NRC made available to the public a 26-page report that preliminarily concludes that Diablo Canyon could withstand a quake from the newfound fault.
“Taking the results of the deterministic analyses as a whole and the current level of uncertainty, the postulated Shoreline Fault will not likely cause ground motions that exceed those for which the plant has already been analyzed,” the report concluded.
Since the first of the year, powerful earthquakes in Haiti and Chile have caused widespread damage and loss of life. Numerous local residents have told the NRC that they find the recent quakes combined with the county’s high seismic potential to be very worrisome.
Reach David Sneed at 781-7930.